Patent Document 1 discloses technology considered to be relevant to the present invention as technology to control a fluid such as a coolant of the engine. Patent Document 1 discloses a cooling system of an internal-combustion engine that sets a high water temperature or a low water temperature by using a high-temperature thermo-valve and a low-temperature thermo-valve.
In addition, Patent Documents 2 through 4 disclose technology related to a failure of a thermostat as technology considered to be relevant to the present invention. Patent Document 2 discloses an engine cooling system failure detecting device that detects a failure of a thermostat. Patent Document 3 discloses a cooling control system of an internal-combustion engine that circulates a cooling medium through a cyclic path having a heat exchanger that releases heat when a failure occurs in a thermostat valve. Patent Document 4 discloses a cooling system of an engine that includes an electric thermostat that opens and closes in accordance with higher temperature between temperature of cooling water and temperature of an electric heater to open and close in accordance with the temperature of cooling water even when a failure occurs in the electric heater.